Catalogs >
Analog Devices >
Current Sense Amplifiers AD22057

Current Sense Amplifiers AD22057
8Pages

Catalog excerpts

FUNCTIONAL BLOCK DIAGRAM AD22057 OUT GND IN+ IN– +VS OFS A1 A2 A1 A2 REV. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. a Single-Supply Sensor Interface Amplifier AD22057 GENERAL DESCRIPTION The AD22057 is a single-supply difference amplifier for amplifying and low-pass filtering small differential voltages (typically 100 mV FS at a gain of 40) from sources having a large commonmode voltage. Supply voltages from +3.0 V to +36 V can be used. The input common-mode range extends from below ground to +24 V using FEATURES Gain of 320. Alterable from 31 to 3160 Input CMR from Below Ground to 63 (VS – 1 V) Output Span 20 mV to (VS – 0.2) V 1-, 2-, 3-Pole Low-Pass Filtering Available Accurate Midscale Offset Capability Differential Input Resistance 400 kV Drives 1 kV Load to +4 V Using VS = +5 V Supply Voltage: +3.0 V to +36 V Transient Spike Protection and RFI Filters Included Peak Input Voltage (40 ms): 60 V Reversed Supply Protection: –34 V Operating Temperature Range: –408C to +1258C APPLICATIONS Current Sensing Motor Control Interface for Pressure Transducers, Position Indicators, Strain Gages, and Other Low Level Signal Sources Accelerometers a +5 V supply with excellent rejection of this common-mode voltage. This is achieved by the use of a special resistive attenuator at the input, laser trimmed to a very high differential balance. Provisions are included for optional low-pass filtering and gain adjustment. An accurate midscale offset feature allows bipolar signals to be amplified. AD22057 SINGLE-POLE LOW-PASS FILTERING, GAIN: 40 POWER DARLINGTON 100mV 200kV C +5V ANALOG OUTPUT 4V PER AMP CORNER FREQUENCY = 0.796Hz-mF ANALOG GROUND SOLENOID LOAD +VS (CAR BATTERY) CMOS DRIVER CHASSIS Figure 1. Typical Application Circuit for a Current Sensor Interface One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 © Analog Devices, Inc., 1999

Open the catalog to page 1

ORDERING GUIDE Model Temperature Range Package Descriptions Package Options AD22057N –40°C to +125°C Plastic DIP N-8 AD22057R –40°C to +125°C Plastic SOIC SO-8 AD22057R-Reel –40°C to +125°C Tape and Reel SO-8* *Quantities must be in increments of 2,500 pieces each. AD22057–SPECIFICATIONS –2– REV. A (TA = +258C, VS = +5 V, VCM = 0, RL = 10 kV unless otherwise noted) Parameter Comments Test Conditions Min Typ Max Units INPUTS (PINS 1 AND 8) +CMR Positive Common-Mode Range TA = TMIN to TMAX +24 V CMR Negative Common-Mode Range TA = TMIN to +85°C –1.0 V CMRRLF Common-Mode Rejection Ratio f £ 10...

Open the catalog to page 2

AD22057 REV. A –3– ABSOLUTE MAXIMUM RATINGS* Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . . +3.0 V to +36 V Peak Input Voltage (40 ms) . . . . . . . . . . . . . . . . . . . . . . +60 V VOFS (Pin 7 to Pin 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . .+20 V Reversed Supply Voltage Protection . . . . . . . . . . . . . . . –34 V Operating Temperature . . . . . . . . . . . . . . . . –40°C to +125°C Storage Temperature . . . . . . . . . . . . . . . . . . –65°C to +150°C Output Short Circuit Duration . . . . . . . . . . . . . . . . Indefinite Lead Temperature Range...

Open the catalog to page 3

AD22057 –4– REV. A Figure 3 shows a general method for trimming the gain, either upward or downward, by an amount dependent on the resistor, R. The gain range, expressed as a percentage of the overall gain, is given by (10 MW/R)%. Thus, the adjustment range would be ±2% for R = 5 MW; ± 10% for R = 1 MW, etc. AD22057 +IN OFS +VS OUT –IN GND A1 A2 VDM VCM R (SEE TEXT) VDM = DIFFERENTIAL VOLTAGE, VCM = COMMOM-MODE VOLTAGE ANALOG OUTPUT 6GAIN ADJUST 20kV MIN ANALOG COMMON Figure 3. Altering Gain to Accommodate Transducer Scaling Error In addition to the method above, another method may be used...

Open the catalog to page 4

AD22057 REV. A –5– frequency will increase; it should be calculated using the parallel sum of the resistor and 100 kW. AD22057 +IN OFS +VS OUT –IN GND A1 A2 VDM VCM ANALOG OUTPUT ANALOG COMMON CORNER FREQUENCY = 1 2pC 3 100kV THAT IS, 1.59Hz-mF (C IS IN FARADS) C Figure 6. Connections for Single-Pole, Low-Pass Filter If the gain is raised using a resistor, as shown in Figure 5, the corner frequency is lowered by the same factor as the gain is raised. Thus, using a resistor of 200 kW (for which the gain would be doubled) the corner frequency is now 0.796 Hz-mF, (0.039 mF for a 20 Hz corner)....

Open the catalog to page 5

AD22057 –6– REV. A To produce a full-scale output of +4 V, a gain ´40 is used, adjustable by ±5% to absorb the tolerance in the sense resistor. There is sufficient headroom to allow at least a 10% overrange (to +4.4 V). The roughly triangular voltage across the sense resistor is averaged by a single-pole low-pass filter, here set with a corner frequency of fC = 3.6 Hz, which provides about 30 dB of attenuation at 100 Hz. A higher rate of attenuation can be obtained by a two-pole filter having fC = 20 Hz, as shown in Figure 11. Although this circuit uses two separate capacitors, the total...

Open the catalog to page 6

AD22057 REV. A –7– APPLICATION HINTS Frequency Compensation As are all closed-loop op amp circuits, the AD22057 is sensitive to capacitive loading at its output. However, the AD22057 is sensitive at higher output voltages due to nonlinear effects in the rail-to-rail design of the buffer amplifier (A2). In this amplifier the output stage gain increases with increasing output voltage. This behavior does not affect dc parameters such as gain accuracy or linearity; however, it can compromise ac stability. When operating from a power supply of 5 V or less (and, therefore, VOUT < 5 V), the...

Open the catalog to page 7